Fix macOS build error.

1. fix #14774.
Change the defconfig of libcxxtest and select libcxxabi by default to
fix sim:libcxxtest build in macOS CI can't find cxxabi.h.

2. fix #15491.
libcxxabi cannot be used with uclibc, so when compiling macos sim, libcxxabi cannot be selected by default in Kconfig.

Signed-off-by: cuiziwei <cuiziwei@xiaomi.com>

Author: cuiziweizw

boards/sim/sim/sim/configs/libcxxtest/defconfig

@@ -44,6 +44,7 @@ CONFIG_IDLETHREAD_STACKSIZE=4096
 CONFIG_INIT_ENTRYPOINT="nsh_main"
 CONFIG_IOB_NOTIFIER=y
 CONFIG_LIBCXX=y
+CONFIG_LIBCXXABI=y
 CONFIG_LIBC_ENVPATH=y
 CONFIG_LIBC_EXECFUNCS=y
 CONFIG_LIBC_LOCALE=y

libs/libxx/Kconfig

@@ -71,7 +71,6 @@ if !LIBCXXMINI
 
 choice
 	prompt "C++ low level library select"
-	default LIBCXXABI if ARCH_SIM && HOST_MACOS
 	default LIBSUPCXX_TOOLCHAIN
 
 config LIBCXXABI